1. Field of the Invention
The invention concerns a sponge made of cellulose and a process for producing same.
2. Description of Related Art
Ullmann's Encyklopadie der technischen Chemie [Encyclopedia of Industrial Chemistry], 3.sup.rd edition (1967), vol. 18, pp. 175-177, describes a method of producing spongy cellulose structures, where layers of pulp are swollen in a 15-20% NaOH solution that is present in excess. Then after a period of time, sodium cellulose is formed. The sodium hydroxide solution is then expressed; it contains in dissolved form hemicelluloses that would otherwise have an interfering effect on the following process steps. The remaining pressed cake in ground form is treated with carbon disulfide, forming cellulose xanthogenate, which dissolves smoothly in a NaOH solution, in which it is degraded after a period of time, with a reduction in the average degree of polymerization (DP). Depending on the grade of pulp used and the storage time, the DP is reduced from 800-1200 to 200-600.
The DP is defined as the average number of individual cellulose molecules of which a cellulose polymer chain is composed on the average.
The alkaline xanthogenate solution is then mixed with pore-forming Glauber's salt, cotton fibers and optional pigment and the mixture is stirred or kneaded until all the components are distributed uniformly. Then a mold that has closed walls and corresponds to the shape of the sponge is filled with the mixture and the mold is closed, but the closure still allows the liquid phase of the mixture to run off.
The mass in the mold is boiled for several hours in a coagulation bath at 100 C. The xanthogenate is cleaved and the pore-forming salt is leached out, forming a spongy structure in the mold. This spongy structure is washed in water and brought in contact with a small amount of 1% sulfuric acid solution to reduce the residual organic carbon disulfide and hydrogen sulfide compounds.